1. Field of the Invention
The invention relates to a wave spring holding structure and a frictional engagement apparatus.
2. Description of the Related Art
In a frictional engagement apparatus used in an automatic transmission for a vehicle or the like, a ring-shaped disc spring is disposed between a multiple-disc clutch and a piston that controls engagement of the multiple-disc clutch, to absorb shock when the clutch is engaged. For example, Japanese Patent Application Publication No. 2005-282807 (JP-A-2005-282807) and Japanese Patent Application Publication No. 9-303455 (JP-A-9-303455) describe technologies relating to a conventional disc spring.
The conventional disc spring is a complete ring in which no cut surface is formed in a circumferential direction thereof. The conventional disc spring is manufactured by a punching process, using a press machine and the like. Therefore, the utilization ratio of a material is low, and thus, the cost is increased. Accordingly, there is proposed a spring (a so-called wave spring) having a C-shape, which is formed by bending a belt-shaped spring material, and in which crest portions and recessed portions are alternately formed in a circumferential direction of the spring material (for example, refer to Japanese Patent Application Publication No. 7-248035 (JP-A-7-248035)). Because the wave spring is formed using the belt-shaped spring material cut into an appropriate length, the utilization ratio of the material is significantly improved, as compared to the conventional disc spring formed by a press punching process.
An arc-shaped snap ring, which includes a gap formed at a portion of the snap ring in the circumferential direction thereof, may be employed as one of two mating members between which the wave spring is held. In this case, when the wave spring rotates with respect to the snap ring, an end portion of the wave spring may enter the gap formed in the snap ring, and the function of the wave spring may be impaired.